1. Field
This invention relates to the solvent extraction of hydrocarbon materials from inorganic matter such as from oil spills, tar sands, sludge ponds and the like and the recovery of solvent from the separated hydrocarbons. More particularly, this invention relates to an apparatus and process for the processing of tar sands and the remediation of oil spill sites and sludge ponds or other hydrocarbon contaminated locations using a low boiling chlorinated solvent and the subsequent recovery of solvent from the separated hydrocarbons. This invention also relates to the separation of a liquid having a lower vapor pressure from a liquid having a higher vapor pressure and to a flashing apparatus for accomplish said separation.
2. State of the Art
It is well known that there are large deposits of bituminous hydrocarbons throughout the world, particularly in Canada and the United States. These are commonly referred to as tar or oil sands. The exact bitumen composition and sand particle envelopment, e.g. with either water or oil surrounding the sand particles, may vary from site to site but all are susceptible to solvent extraction of the bitumen from the inorganic particles and the need to dispose of the lean sands in an environmentally acceptable manner.
There are numerous processes which have been developed and patented relating to the processing of such deposits using various extraction means including hot and cold water extraction; solvent extraction; combinations of water and solvent extraction; oleophilic sieve separations and the like.
In addition, there is a constantly escalating environmental contamination problem associated with the deliberate or accidental deposition of hydrocarbons of various types on both land and sea. For example, petroleum dumps, drilling rig sludge ponds, oil refineries, retail gas stations, chemical plants, superfund sites, pipeline and tanker spills on both land and sea all contribute to the environmental pollution of the sites where hydrocarbons are deposited and may lead to pollution of other locations due to spillage into waterways or migration to surrounding soils unless removed and/or contained.
Thus far, most soil remediation processes have involved either hauling the hydrocarbon contaminated soil to a more remote storage site or dump or the building of a containment barrier around and/or over the contaminated site. Little had been done to actually remediate or restore contaminated soils to a clean or original condition. Some remediation suggestions have involved burning off the hydrocarbons, bioremediation and water or solvent extraction. Burning only exacerbates problems of pollution and water or water/solvent extraction processes contaminates the water. Further, many sites needing remediation are not near water sources. Solvent recovery processes often require the addition of one or more solvents which cannot then be completely or economically separated from the hydrocarbon they are to extract resulting in loss of both solvent and extracted hydrocarbon.
Because of similarities between hydrocarbons deposited on or soaked into soils and the naturally occurring tar sand deposits, processes suitable for the extraction of bitumen from tar sands seem likely methods for also cleaning up soil sites contaminated by spilled or residual hydrocarbons. Since many sites needing remediation are not conveniently located near water supplies, solvent removal processes are preferred if practical.
Blaine, U.S. Pat. Nos. 4,046,669 and 4,057,485, disclose a process for extracting oil from tar sands utilizing a chlorinated solvent such as monochloroethane, dichloroethane, trichloroethane or tetrachloroethane.
Gagon, U.S. Pat. No. 4,342,639, is drawn to a process of removing bitumen from tar sands using a chlorinated solvent, preferably methylene chloride, that is heavier than water. The solvent extraction of bitumen from the sand takes place under a blanket of water, preferably at ambient pressure and at a temperature which is below the boiling point of the solvent at the pressure used. The bitumen rich solvent solution is withdrawn from the lower portion of the extraction chamber and the cleaned sand is washed by passing through the water blanket layer and disposed of. The bitumen rich solvent solution is subjected to flash evaporation to separate the bitumen from the chlorinated solvent in an evaporation chamber maintained under a negative pressure. The solvent vapors removed overhead are placed under positive pressure by a compressor and introduced into a condenser.
Haschke et al., U.S. Pat. No. 4,532,024, summarizes a compendium of solvent extraction systems for treating tar sands. Predominant among these methods is the use of chlorinated hydrocarbon solvents. Most of these are deficient in that they do not provide for the complete removal of the solvent from the extracted bitumen prior to further refining. The means mentioned for separation of solvent from the bitumen include flash distillation and conventional evaporation and ambient temperature evaporation. It is concluded by Haschke et al. that, of the chlorinated solvents, methylene chloride has the best overall properties for extraction of bitumen because it behaves as a nonflammable solvent, has the greatest solvency power of solvents tested, has a workplace safety standard which can be achieved with good work practices and is one of a few solvents that the EPA has determined to have insignificant photochemical reactivity and consequently its emissions may not have to be controlled under regulatory VOC emission regulations. A primary thrust of this patent is the removal of methylene chloride from the bitumen in a two step process. The first step involves the simple distillation of the major portion of the solvent followed by a second step which uses a high-boiling stripper diluent solvent to remove the residual solvent. It is stated that, with the proper stripper diluent solvent, essentially complete removal of residual halogenated solvent is accomplished by monitoring the temperature of the exiting bitumen product stream. In other words, it is desirable to choose a stripper diluent solvent that has an acceptable boiling point to strip out all residual chlorinated hydrocarbon solvent. Not all of the stripper solvent is removed from the bitumen and some may be deliberately left in or even added to control the viscosity of the bitumen for purposes of transportation and refining. Suitable stripper diluents are stated to be intermediate boiling hydrocarbon fractions such as mineral sprits, Stoddard solvent, xylene, kerosene and #2 diesel oil. Also, pure components, such as ethyl benzene which has a suitable boiling point, can be used. This process has the disadvantage that a stripper diluent must be transported to the remediation site or tar sand extraction site and also is not completely recovered but incorporated into the recovered contaminant hydrocarbon or extracted tar sand. It is both expensive and inefficient to require the addition of an extra component in order to recover and remove the extracting chlorinated hydrocarbon solvent Moreover, to remove the chlorinated solvent it is necessary to heat the solution containing the stripper solvent to temperatures above the boiling point of the stripper solvent. This required the heating of relatively large amounts of solution, including the bitumen recovered from the tar sand extraction, to temperatures well above the boiling point of water, e.g. from about 130.degree. to 160.degree. C. (265.degree.-320 .degree. F.).
It would therefore be highly beneficial to develop a process for the efficient removal of hydrocarbons from soils in a remediation process or in the extraction of bitumen from tar sands wherein essentially complete removal of the solvent from the hydrocarbon or bitumen could be obtained without the need of extra processing steps and wherein the solvent could be recovered almost quantitatively in a closed system without environmental damage to the surrounding atmosphere.